The invention pertains to a needle protector for sewing machines of the double chain stitch type in which the looper is caused to travel about the needles in a substantially elliptical pathway.
This needle protector is of the movable type and is actuated downstream of the needles by being operatively connected to one of the two movements which together effect orbital travel of the machine's looper.
The movable needle protector element according to the invention is carried on a bracket member which is pivotably connected to a fixed support element mounted in the base of the machine and is provided with connecting means operatively associated with the looper so that said movable needle protector element is caused to move into close proximity with the needles during the initial movement of the looper at the start of a new stitch.
The invention is applicable to a sewing machine of the double chain stitch type and, more particularly, to a machine having a reciprocating needle bar with at least one needle and at least one looper cooperating with the needle to form stitches. Actuating means are provided which cause the looper to reciprocate transversely of the direction of travel of a workpiece being sewn and simultaneously in a direction parallel with the workpiece direction of travel whereby the combination causes said looper to travel in an elliptical pathway. These machines also include a transport device having at least one feed dog that functions during seaming and downstream therefrom and operatively associated therewith has a needle protector element which serves to maintain the operating phase positions constant between the needle and the looper during the formation of each stitch.
Sewing machines of the type described have the looper and its associated support element mounted on a looper shaft which is operatively connected to the actuating means referred to above for causing said looper to perform its intended function. This so-called looper shaft can be subjected to oscillatory motion about its axis which is perpendicular to the direction of workpiece advance and to simultaneously subject the looper to movement parallel to the direction of workpiece advance. The sole portion of the looper support is acted upon by means such as occurs in the Rimoldi Class 264 sewing machines. The looper shaft can also be acted upon so that it oscillates about its axis and simultaneously translates along the same axis such as occurs in the Rimoldi Class 183 sewing machines. In both classes of machines, the needle protector is caused to reciprocate forwardly and rearwardly in a direction parallel with the advance of a workpiece during seaming and its movement is commonly accomplished by the feed dog to which it is operatively connected. The linkage between the needle protector element and the feed dog is determined by the fact that the rearward displacement of the feed dog is in the same direction as that which the needle protector has to be moved to approach the needle in timed sequence with movement of the looper into close proximity with the needle. Such linkage is also determined by the fact that a portion of the feed dog is disposed downstream of the needle whereat it is adapted to support the needle protector element.
Although the synchronization of movements of the feed dog and the needle protector element connected thereto as well as the looper are such that these elements perform their intended functions as desired. The linkage between said feed dog and needle protector element is responsible for what is considered a very undesirable condition. This condition presents itself when it is desired to change the length of the stitches being formed, for any such change, it is necessary to adjust the relative position of the needle protector element to maintain unchanged the stroke position of the needle relative to the looper. Additionally, and as is well known to those conversant in the art, the feed dog is subjected to a reciprocating motion which has no means for counteracting for variations in the movement of said feed dog and which is accentuated with increases in sewing machine speed. This deficiency of the transport device in general is greatly accentuated when the needle protector element is fixedly attached to the feed dog.